On Wed, 03 Aug 2005 00:03:02 GMT, "Jerry Foster"
wrote:
"Eric R Snow" wrote in message
.. .
On Tue, 02 Aug 2005 00:40:36 -0500, Don Foreman
wrote:
http://users.goldengate.net/~dforeman/conduit/
Field-expedient tight bends in EMT for making stuff. Not pretty, but
it works.
Nice job Don. Another method which works, and doesn't wrinkle the
metal, is to heat the area almost red or just till it starts being
red, and spray water on it. Do this a few times and the bend is very
controllable. I learned about this method in welding class. I saw it
being done at Lockheed Shipyard in Seattle before it closed. They were
using huge torches to heat 3 inch thick steel pie shaped sections.
These were being curved so they could be welded into a 1 half
spherical shape. It eventually was welded to the hull under the prow
of a ship. I'm sure you've seen an empty ship riding way out of the
water and there is this bulbous thing sticking out of the hull. Also,
we were shown a movie of the men who bent the legs to the Space Needle
using the same method. After seeing this I had to try it for myself
and have bent and straightened both mild steel and stainless steel.
Eric
Could you provide a few more details? I am assuming you spray a small
quantity of water on the inside of the curve to be bent, correct?
Jerry
Greetings Jerry,
What happens is that the heated metal expands. Since the hot metal is
plastic it will move as far as it can, which is where the metal is too
cool to deform. Then when the hot area is cooled the space between the
molecules shrinks and the metal contracts. If left to cool slowly the
displaced metal will move back into it's original shape. But rapid
cooling prevents this so instead the metal shrinks. So rapid cooling
is important. The metal you are shrinking must be able to go through
these hot and cold cycles without damage. So mild steel is a good
candidate for this process. It takes practice but not that much and
once mastered it can be real useful. Another place this method is used
is with removing dents from sheet metal, as in auto bodies. Big dents
in an auto body stretch the metal and to avoid using bondo to fill the
depression heat shrinking the area is sometimes used to fix these
dents. I've done it with a torch and a wet rag. Sheet metal is so thin
that a wet rag can cool the area fast enough.
ERS